Radius and ellipse dresser for grinding wheels



Jan. 27, 1959 F. E. BUCZKOWSKI 2,

RADIUS AND ELLIPSE DRESSER FOR GRINDING WHEELS Filed Dec. 5, 1956 2 Sheets-Sheet 1 2 I INVENTOR.

A5 BY Z :5 M

l EZ/YZZTEHdZZ Jan. 27, 1959 F. E. BUCZKOWSKI RADIUS AND ELLIPSE DRESSER FOR GRINDING WHEELS Filed Dec. 5, 1956 2 Sheets-Sheet 2 R Z 2 m M v i m u m u n i ,M n a n W h F 4 9 7 4 1 1 14, TZ g w A FILE t M United States Patent RADIUS AND ELLIPSE DRESSER FOR GRINDING WHEELS Frank E. Buczkowski, Detroit, Mich. Application December 5, 1956, Serial No. 626,445

Claims. (Cl. 125-11) This invention relates to an abrasive wheel dresser and more particularly to a wheel dresser adapted to be operated to dress either a true radius or a true ellipse on the periphery of a grinding wheel.

In the prior art there may be found a number of abrasive wheel dressers which may be operated to dress a true radius on the periphery of a Wheel. In general, radius Wheel dressers are characterized by the provision of simple means for setting the apparatus so that the wheel dressing diamond nib will travel in a path generating the desired radial surface, the setting being accomplished with vernier devices or gauge blocks. The generation of. a more complex curve, such as an ellipse, is beyond the capability of an ordinary radius wheel dresser and it has been necessary to resort to more complicated devices such I as those utilizing templets or the like in order to achieve the desired result. It is an object of the present invention to provide a Wheel dresser having the characteristic of anordinary radius wheel dresser in that it may be readily set with vernier devices or gauge blocks not only to generate true radial curves but also to generate true elliptical curves on the periphery of abrasive wheels.

In its illustrated embodiment, the invention in brief consists of a grinding wheel dressing unit comprising a base structure on which a trammel arm means is slidably supported for oscillatory movements. The trammel arm means carries a conventional wheel dressing device, such as a diamond nib carried in a suitable holder. The move-' The magnitude of the elliptical path travelled by the diamond nib is dependent on the distance between the diamond nib andone of the control elements and the distance between said one control element and the otherof said control elements. In terms of minor and major axes of the elliptical path, one-half the minor axis, hereinafter sometimes referred to as the semi-minor axis, is equal to the distance between the diamond nib point and one of said control elements. One-half the major'or the semi-major axis is equal to the semi-minor axis plus the distance between the one control element and the other. When the distance between the control elements is zero, the semi-major and semi-minor axes are equal and the path travelled by the diamond nib is no longer elliptical but is radial.

It is a feature of the construction and arrangement of the wheel dressing unit embodied in the present invention in that means are provided for accurately determining and controlling the relative positions of the diamond nib and the control elements: so thatthey maybe set to give;

ICC

a predetermined radial or elliptical contour to a grinding wheel.

Further objects and advantages and the features of construction embodied in the present invention Will be apparent from the following description and appended claims, reference being had to the accompanying draw ings forming a part of this specification wherein like reference numerals designate corresponding parts in the.

several views.

Fig. 1 is a plan view of the wheel dresser embodying the Fig. 4 is a plan elevation in part similar to Fig. 1 but" illustrating thewheel dresser set-up to generate an elliptical curve on an abrasive wheel.

Fig. 5 is a side elevation in part sectional of Fig. 4.

Fig. 6'is a fragmentary view illustrating the diamond nib holder in a second position.

Before explaining in detail the presentin'vention, it is i to be understood that the invention is not limited in its; application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways.

In the drawings there is illustrated, by way of example,

a preferred embodiment of the abrasive wheel dresser 10 7 adapted to dress the peripheral face of a grinding Wheel 11. The wheel dresser 10 comprises a'base structure, generally designated 12. The base structure 12 com-' prises a rectangular plate 13 having a centrallylocated longitudinally extending'slot 14, which slot will herein- 1 after be referred to as. the vertical axis slot. Overlying the plate 13 is a wear plate 15 which in size and shape has the'outline of the base structure 12 as viewed in'Fig; 1. The plate 15 is provided with a slot 16 which corresponds to the vertical axis slot 14 but is slightly larger in'size. The plates 13 and 15 are secured to each other in any convenient manner, as by bolts (not shown).

The wear plate 15 carries on its upper surface a pair of spacer blocks 17. The spacer blocks are located at the side edges of the plate 15, as indicated in dotted outline in Fig. 1. The spacer blocks 17 support a plate 18 in parallel spaced relation to the plate 15', the plate 18 having the same general shape as the plate 15. The plate 18 is provided at substantially the left end thereof, as shown in Figs. 1 and 2, with an elongated slot 19 hereinafter referred to as the horizontal axis slot.

,It' will be noted that the longitudinal axis of th horizontal axis slot 19 is perpendicular to the longitudinal axis of the vertical axis slot 14. It will be further noted that the edge 20 of the horizontal axis slot 19 is in exact alignment, with the end edge 21 of the vertical axis. slot 14. ,The horizontal axis slot 19 is twice the length of the 1 vertical axis slot 14. The reasons for these relationships will hereinafter be explained.

Overlying the plate 18 is a wear plate 22 of substantion of castings and plates. Since thesedetails. of fabrica-Q tion do not control the principle of operation, it is believed that the foregoing description and explanation is adequate for an understanding of the invention.

Mounted on the' base structure 12 is a trammel arm device, generally designated24. This device comprises an. upper trammel arm 25 and alower trammel arm 26. The upper trammel arm 25 is provided with-a dependmg spacer portion 27 to which the lower trammel arm 26 is keyed and secured in any convenient manner, as by a bolt'2 8.

"The :right end I29 of the lower trammel arm 26 is slida bly contained between the two spaced plates 15 and 18. At this end the arm 26 is provided with an aperture 30 located on the longitudinal axis of the arm. The aperture 30 has tightly fitted therein an elongated pin 31 which projects through slot 16 of the plate 15 into the vertical axis .slot 14. The fit of the pin 31 Within the slot 14 is suchthat the pin is freely movable but is accurately guided in its movements relative to the slot walls. The pin 31 is hollow and is adapted to receive an alignment pin 32, for a purpose to be hereinafter explained.

The upper trammel arm 25 is supported and guided by a block 33 movable on the upper surface of the plate 22. The block 33 is provided with a depending hollow pin 34, see Fig. 2. This pin 34' projects through the slot 233 in the plate 22 into the horizontal axis slot 19 in the plate 18. The fit of the pin 34 in the slot 19 is also such that the pin is freely movable in and accurately guided bythe slot walls as the block 33 is moved laterally across the plate 22 surface, as will be explained.

The trammel arm 25 is square sided on the lower portion 35 thereof and is slidable between the side walls 36 and 37 of the block 33. The side face of the portion 35 isprQVided with a longitudinally extending T-slot 38 engaged by a T-shaped key 39. The key 39 is provided with a threaded shank 40 projecting through an aperture in the side wall 37. A knurled nut 41 is threaded on the key shank 40 and, upon being turned in the proper direction, is effective to pull the key 39 toward the block sidewall 37. The clamping action of the key 39 against the walls of the slot- 38 is effective to lock the trammel arm 25 against movement relative to the block 33.

,The upper portion 42 of the trammel arm 25 is'in the nature of a dovetailed guideway along which operates a slide 43 provided with a complementary dovetailed groove formation 44. The slide 43 carries a thumb Wheel. 45 attached to a set screw 46 adapted to project through the slide into bearing engagement with the upper surface of the trammel arm 25. By turning the thumb wheel 45 in the appropriate direction, the slide 43 may be locked to the trammel arm 25 The slide 43 carries the upright dressing arm 47, the lower end of the arm being removably keyed to or mounted on the slide 43 in any convenient manner. Near its upper end, the dressing arm is provided with a socket 48 for reception of a diamond holder 49 which is kept in place by a set screw 50 having a knurled cap 51 thereon. The holder 49 is positioned in the dressing arm in such a manner that the tip of the diamond 52 is vertically aligned with the plane of the face 53 of the dressing arm. This is done by setting a straight edge against the face 53 of the arm and positioning the diamond tip thereagainst.

It will be noted that the block 33 is provided on one side with an upstanding projection 54. The projection 54 is provided with two accurately machined parallel faces 55 and 56, the faces being accurately spaced a known dimension. The face 55 is accurately aligned with the center of the hollow pin or projection 34 on the block 33, the plane of the face 55 and the vertical axis of the pin 34being the zero reference plane. The slide 43 is providedwith a corresponding projection 57 also having two accurately machined parallel faces 58 and 59. These faces are also accurately spaced a known dimension.

When the dressing arm 47 is mounted on the slide 43 as shown in Fig. 2, the plane of the face 58 is coincident with the plane of the reference face 53. When the slide 43 is positioned on the upper or dovetailed guideway portion 42 of the upper trammel arm 25 so that the face 58 of its projection 57 abuts the face 55 of the projection 54, the diamond tip 53 will be at zero displacement relative to the center of the pin 34 on the block 33.

The diamond tip 52 may be accurately located relatively to the center of the :pin 34 by the use of 'guage blocks between the reference faces 55 and 58, by the use of inside calipers between the same reference faces-or by the use of outside calipers measuring the distance between the reference faces 56 and 59, in the latter case due allowance being made for the thickness of the projections 57 and 58.

it will be noted that the plate 13 is provided with a longitudinally extending bore 60 (Fig. 2) having a push rod 61 slidably mounted therein; The push rod 61'i's urged toward the .pin 31 by a coil spring '62 retained in the bore 60 by a plug 63. The push rod 61 and spring 62 function .as a take-up device to negative even the small amount of play inherent in any structure despite the accuracy with which the parts may be machined.

The foregoing substantially completes the structural description of the invention. The reasons for some of the structural relationships will now become apparent. as the operation of the wheel dresser is explained.

First, the'wheel dresser 10 will be considered as a'r'adiul dresser. When so used the dresser 10 will appear as illustrated'in Figs. 1 to 3 inclusive. That is, the alignment pin 32 projects through the hollow pins 31 and 3.4. The two pins 31 and 34 are thus vertically aligned; and neither may be moved along the longitudinal axis of its related slot. inhibit movement of the coupled pins 31 and 34 ina direction parallelto the longitudinal axis of the slot 20 ;.tional practice.

' pins 31 and 34 from each other.

and the side walls of the slot 20 inhibit movement of:

the coupled :pins in a direction parallel. to the longitudinal axis of the slot 14.. The result is that the trammel. arm. device 24 is limited to swinging movement with. the axis; of the aligned pins 31 and 34 as the center of rotae tion.

The diamond point 52 is thus restricted to travel in a circular path having a radius as determined by the. distance between the reference projections 54 and 57.

The set-up: of the dresser ltlfor dressing a male radius on the peripheral facev of a wheel 11 follows conven- The dresser 1th is placed on the mag.

netic chuck of a surface grinder (not shown), provision being made to space the plate 13 above the chuck surface a suflicient distance to accommodate the knurled head of the alignment pin 32. The dresser is placed in ;proper .pa-rallel alignment with the back rail of the chuck table. ward or downward until the diamond point 52 is in alignment witha horizontal plane passing through the 'center of the wheel spindle. Assuming that the tip of the diamond is in operative engagement with the peripheral face of the wheel 11 as it rotates, it is only necessary to manually swing the trammel arm device 25 about the center of swinging movement as determined by the aligned pins 31 and 34. The diamond tip 52 will thendress the wheel to a desired radius equal to the displacement of the diamond tip from the zero reference plane.

The dressing of a true ellipse on the periphery of the wheel 11 using the dresser 1t) embodying the present invention is substantially no more complicated than the foregoing procedure for dressing a true radius. To change the dresser 1th from a radius dresser as illus trated in Figs. 1 to 3 inclusive, it is only necessary to withdraw the alignment pin 32 thereby uncoupling the With the T-shaped key 39 loosened, the trammel arm device 24 may be shifted relative to the block 33'. The trammel arm de vice may be shifted from its Fig. 2 position to the right to Y The side walls of the vertical axisslot 14 The chuck table of the machine is moved upthe position shown in Fig. 5, the range of such movement pin 31 attached to the trammel arm 26 is movable. Normally the trammel device will be shifted to the right to some position intermediate that shown in Figs. 2 and 5. .With the trammel arm device 24 positioned so that the pin 31 is displaced to the right of the pin 34 and the dressing arm 47 displaced to the left o fthe zero reference plane, the samezero reference plane described in the operation of the dresser as a radius dresser, the diamond point will travel in an elliptic path if the trammel arm device 25 is manually swung ,clockwise or counterclockwise as viewed in Figs. 2 and 4. i

The reason the diamond point will travel an elliptical path may be explained as follows: As may be gathered from the designation of the arm structure 25 as a trammel arm device, the dresser when used to dress an elliptical surface on a wheel 11 operates on the elliptic trammel principle. A trammel is defined as an instrument for drawing ellipses, one part of which is essentially a cross with two grooves at right angles to each other, the other being a beam carrying two pins, each slidable in one of the grooves and also the describing pencil. In the illustrated embodiment of the invention, the cross is represented by the vertical axis groove 14 and the horizontal axis groove 20. Since only half an ellipse is to be described, the vertical axis groove 14 terminates at the horizontal axis groove 20. The beam is represented by the trammel arms 25 and 26. The pins are represented by the pin 31 attached to the trammel arm 26 and slidable in the groove 14 and by the pin 34 which may be fixed relative to the arm 25 through the block 33 and slidable in the horizontal axis groove 20. The describing pencil is represented by the diamond point52.

As will be readily understood from the general theory of operation of an elliptic trammel, if the left end of the trammel arm device 25 is manually grasped and moved so as to cause the pin 34 to travel longitudinally of the groove 20, the pin 31 will also be caused to travel longitudinally' of the vertical axis groove 14 and the diamond point will travel the dot and dash line 64 path thereby generating an elliptical curve. The characteristics of the elliptical curve generated is dependent on two factors. The shorter the distance between the zero reference plane (the plane including the center of the pin 34) to the tip of the diamond 52 the flatter the generated curve. The closer the vertical axes ofv the pins 31 and 34 are placed to each other, the rounder the ellipse becomes. 34 were vertically aligned by the alignment pin 32, the diamond tip 52 moved in a circular path thereby generating a true radius on the periphery of the wheel.

In terms of major and minor axes of an ellipse, the distance from the vertical axis of the pin 31 to the diamond tip 52, when the latter lies on the longitudinal axis of the slot 14, is equal to one-half the major 'axis of the ellipse to be generated. The distance from the vertical axis of the pin 34 to the diamond tip 52 is equal to one-half the minor axis of the ellipse to be generated. When the diamond tip 52 and the vertical axes of the pins 31 and 34 lie in-a common vertical plane no curve is generated. When the distance between the tip 52 and the vertical axis of the pin.31 equals the distance between the tip'52 and the vertical axis of the pin 34, said axes being coincident, a circle or true radius is generated. When the distance between point 52 and the vertical axis of the pin 34 is unequal to the distance be tween the point 52 and the vertical axis of the pin 31,

It will be recalled that when the pins 31 and on the magnetic chuck of the grinding machine so'that it is repositioned, one hundred and eighty degreesfrom the position illustrated in Figs. '4 and 5. However, it is" also necessary to reposition the dresser arm one hundred and eighty degrees relative to the dresser 10 so that it willhe presented to the, wheel 11 as illustrated in Fig.

6. It will be notedfithat the reference face 53 on the dresser arm 47 remains in .the plane of the reference face 58 on the slide 43. Th us, for measuring purposes,

nothing is changed by the one hundred and eighty degree repositioning of the arm 47.

.Returning to Figs. 4 and 5, the procedure in setting up the dresser 10 to dress a specific elliptic curve on the periphery of awheel 11 is as follows: For. example, assume that it is desired to dress a two inch thick wheel with a full semi-elliptical-surface,the minor axis of the ellipse being one-half inch, With the trammel. arm device 24 in its extreme left position, i. e.,'the 'same positionas shown in Fig. 2 (but with the pin 32 removed),

the diamond-point v52 is positioned from the zero reference plane a distance equal to one-half the major axis of the semi-ellipse to be generated. One-half the ma-' to permit the trammel arm 25 and thereby the trammel I arm-device'24 to be moved relative to the block 33. will be apparent that the trammel'arm device 24 is movable only to the right from the position shown in Pig.

2 toward the extreme right position shown in Fig. 5.

However, in'the present assumed problem one-half the minor axis is one-quarter inch, the minor axis being onehalf inch. This means that the vertical axis of the pin 31 must be displaced one-quarter inch to the right of the vertical axis of the pin 34'. With the reference plane or edge 58 fixed to the trammel arm device 24, the simplest way to measure the one-half displacement of the pin 31from the pin 34 is to move the trammel arm device 24 to the right until the reference plane-58 is one-half inch from the reference plane 55. Upon this position being reached, the pin 31 is correspondingly displaced one-quarter inch from the pin 34. Next, the T-shaped key 39 is tightened in the slot 38 locking the trammel arm device to the block 33.

Upon the trammelbeam comprising the trammel arms 25 and 26 being swung, the pins 31 and '34 acting in their respective grooves 14 and 20 will cause the beam to travel in the particular oscillatory movement of an elliptic trammel beam which results in the describing or diamond point generating an ellipse. The periphery of the wheel 11, with the dresser 10 set as described'in the illustrative problem, would be dressed to a semi-elliptical contour, the semi-ellipse having a two inch major axis and a one-quarter inch semi-minor axis.

The practical application of the foregoing may be further illustrated withreference to a radius tool, the whole cutting edge of which forms an arc of a circle ofany specificdiameter. If the angle of the face of the tool ,is

'to the base of the tool. The cutting edge when viewed in the plane of the base of the tool appears as an arc of a true circle. But, when viewed in a plane perpendicular to the end clearance plane, the cutting edge appearsas a. semi-ellipse whose major axis is equal to the diameter I? of the circle of which the cutting edge are forms a part. The semi-minor axis" of the ellipse is equal to one-half the ma or axis (i. e., the radius. of the cutting edge are circle) multiplied by the sine of the quantity 90 minus the end clearance angle. Or, stated another way, the

semi-minor axis equals the valueof the radius multiplied resents onehalf the major axisof the cutting edge which isan arc of a circle having a one-half inch radius or'a one inch diameter. The minor axis equals .500 inch multiplied by cos or .86603 giving 0.433 inch. With the slide 43 securely locked to the upper trammel arm 25, the trammel arm device 24 is moved so that the reference plane 58 is spaced 0.433 inch from the reference plane 55. In other words, the dresser "10 has now been set so that the distance from the diamond point 52 'to the vertical axis of the pin 31 is equal to one-"half the major axis of the desired ellipse or 0.500 inch. The distance from the diamond point 52 to the vertical axis of thehpin 34 is equal to one-half the minor axis -or-0.433- inc es.

By appropriately swinging the trammel arm device "-24- in alternate clockwise and counterclockwise directions as viewed in Fig. 4, the diamond point 52 will generate the desired elliptic periphery on the wheel 11. If the end face of the cutting tool is presented to the'per-i-phery of the wheel so that the plane of the end. face is tangential to the wheel, the Wheel will dress the cutting edge so that it is a true radius when viewed in the plane of the base of the tool.

I claim:

1. A. grinding wheel dressing device comprising 'abase structure, trammel arm means slidable on said basexstructure for oscillatory movement with respect thereto, wheel dressing means carried by said'trammel arm means, said trammel arm means comprising a pair of vertically spaced beams, said base structure being provided with a pair of vertically spaced beam supporting surfaces each provided I with a guide groove, the longitudinal axes of said grooves being at right angles to each other, each beam being provided with a control element slidable in a respective guide groove, and means effective to maintain said cqntrol elements in one selective relative position thereof whereby the trammel arm means is limited to movement such that the wheel dressing means is movable only in a circular path.

2. A grinding wheel dressing device comprising; a base structure, trammel arm means slidable on said base structure for oscillatory movement with respect thereto,

wheel dressing means carried bysaid trammel arm means, said trammel arm means comprising a pair of vertically spaced beams, said base structure being provided with a pair of vertically spaced beam supporting surfaces'each' provided with a guide groove, the longitudinal axes of said grooves being at right angles to each other, each beam being provided with a. control element slidable in a respective guide groove, and means selectively effective to maintain said control elements in a selective relative position thereof whereby the trammel arm means is limited. to movement such that the wheel dressing means is movable only in a circular path or :to maintain said control elements in any other selective relative position thereof whereby the trammel arm means is limited to movement such that the wheel dressing means is movable onlylin an elliptical path.

3. A grinding Wheel dressing, unit comprising a base structure, trammelarm means slidable on said'base struc' ture for oscillatory movement with respect thereto, wheel trammel arm. means comprising a'pairof vertically spaced beams, said base structure being provided with apa-ir of vertically spaced beam supporting surfaces each provided with a guide groove, the longitudinal axes of "said grooves being at right angles to each other, each beam being provided with a' control element slidable in arespective guide groove, and means selectively effective to maintain said control elements in a selective relative position thereof whereby the trammel arm means is limited to movement such that the wheel dressing means is movable only in a circular path or to maintain said control elements in any other selective relative position thereof whereby the trammelarm means is limited to movement such that the wheel dressing means is movable only in an elliptical path, in the latter position the serni-mmor axis of said elliptical path being equal to the "distance between one of the control elements and the operative surface of the wheel dressing means and the semi-major axis being equal to the semi-minor axis plusthe distance between said onecontrol element and the other control element.

-4. A grinding wheel dressing unit compnslng a base structure, trammel armmeans and wheeldressmg means carried by said trammel arm means, said trammel arm means comprising a pair of vertically spaced parallel beams, said base structure being provided with'vertically spaced beam supporting surfaces each provided with a guide groove, the longitudinal axes of said grooves being at right angles to each other, a slide means interposed between one of said beams and its supporting surface, guide means carried by said slide means and the other of 'saidbeams-each slidable ina respective guide -groove, said trammel arm means being movable relative to sand slide means whereby said guide means may be selectively I positionable relative to one another, said guide means when in vertical alignment limiting the trammel arm means t0-movement such that the wheel .dressing means movement is-in a circular path and when out of vertical alignment limiting the "trammel arm means to movement such that the wheel dressing :means movement is man elliptical path.

"5. A grinding wheel dressing unit comprising a base structure, trammel'arm means, and wheel dressingmeans carried by saidtrammel arm means, said trammel arm means comprising a pair of vertically spaced parallel beams, said-base structure being provided wit-h vertically spaced be'atn' supporting surfaces each provided with a guide groove, the longitudinal 'axesof said grooves being at right angles to each other, a slide means interposed between one-of said beams and its supporting surface, guide means carriedby said slide means-and the otherof said beams each slidable'in'a: respective'guide groove, said trammel'armmeans being movable relative tosaidslide means whereby said guide means may be selectively positionable relative to-one another, the difference between the semi-minor and semi-major axes of the curve 'generated. by movement of the trammel arm means being equal to the displacement-between the longitudinal axes of sai'd guide means.

-6. A grinding wheel dressing unit comprising a base structure, trammel armmeans, and Wheel dressing means carried bysaid trammel arm means and adjustablypositionable thereon, said trammel arm means comprising upper and lower spaced parallel beams, said'base structure 'beingjprovided with upper and'lower spaced beam -supporting surfaces, said lower beam supporting'surface being provided with a longitudinallyextending groove and the upper beam supporting surface being provi'ded'with a laterally extending groove, said longitudinally extending groove terminating at one end thereof in alignment with the laterally extending groove and the longitudinal axes of said grooves being at right angles to each other,

,a slide means interposed between said upper beam and. said upper beam supporting surface, pin means carried by said slide means and slidable in said laterally extending groove, pin means carried by said lower beam and slidable in said longitudinally extending groove, said trammel arm means being movable relative to said slide means whereby said pin means may be spaced a selective distance apart from each other along the longitudinal axis of the longitudinally extending groove, said pins means when in vertical alignment limiting the trammel arm means to movement such that the wheel dressing means movement is in a circular path and when out of vertical alignment limiting the trammel arm means to movcn out such that the wheel dressing means movement is in an elliptical path.

7. A grinding wheel dressing unit comprising a base structure, trammel arm means, and wheel dressing means carried by said trammel arm means and adjustably positionable thereon, said trammel arm means comprising upper and lower spaced parallel beams, said base structure being provided with upper and lower spaced beam supporting surfaces, said lower beam supporting surface being provided with a longitudinally extending groove and the upper beam supporting surface being provided with a laterally extending groove, said longitudinally extending groove terminating at one end thereof in alignment with the laterally extending groove and the longitudinal axes of said grooves being at right angles to each other, a slide means interposed between said upper beam and said upper beam supporting surface, pin means carried by said slide means and slidable in said laterally extending groove, pin means carried by said lower beam and slidable in said longitudinally extending groove, said trammel arm means being movable relative to said slide means whereby said pin means may be spaced a selective distance apart from each other along the longitudinal axis of the longitudinally extending groove, said pin means when in vertical alignment limiting the trammel arm means to movement such that the wheel dressing means movement is in a circular path and when out of vertical alignment limiting the trammel arm means to movement such that the wheel dressing means movement is in an elliptical path, in the latter position the semi-minor axis of said elliptical path being equal to the distance between one of the control elements and the operative surface of the wheel dressing means and the' semimajor axis being equal to the semi-minor axis plus the distance between said one control element and the other control element.

8. A grinding wheel dressing unit comprising a base structure, trammel arm means, and wheel dressing means carried by said trammel arm means and adjustably positionable thereon, said trammel arm means comprising upper and lower spaced parallel beams, said base structure being provided with upper and lower spaced beam supporting surfaces, said lower beam supporting surface being provided with a longitudinally extending groove and the upper beam supporting surface being provided with a laterally extending groove, said longitudinally extending groove terminating at one end thereof in alignment with the laterally extending groove and the longitudinal axes of said grooves being at right angles to each other, a slide means interposed between said upper beam and said upper beam supporting surface, hollow pin means carried by said slide means and slidable in said laterally extending groove, hollow pin means carried by said lower beam and slidable in said longitudinally extending groove, said trammel arm means being movable relative to said slide means whereby said pin means may be spaced a selective distance apart from each other along the longitudinal axis of the longitudinally extending groove, said hollow pin means when in vertical alignment limiting the trammel arm means to movement such that the wheel dressing means movement is in a radial path and when out of vertical alignment limiting the trammel arm means to movement such that the Wheel dressing means movement is in an elliptical path, and removable means insertable through one of said hollow pin means into the other of said hollow pin means to couple the same in vertical alignment.

9. A grinding wheel dressing device comprising a base structure, trammel arm means slidable on said base structure for oscillatory movement with respect thereto, wheel dressing means carried by said trammel arm means, said trammel arm means comprising a pair of vertically spaced members, at least one of said members being a beam, said base structure being provided with a pair of vertically spaced member supporting structures each provided with a guide groove, the longitudinal axes of said grooves being at right angles to each other, each beam being provided with a control element slidable in a respective guide groove, and means effective to maintain said control elements in one selective relative position whereby the trammel arm means is limited to movement such that the wheel dressing means is movable only in a circular path.

10. A grinding wheel dressing device comprising a base structure, trammel arm means slidable on said base structure for oscillatory movement with respect thereto, wheel dressing means carried by said trammel arm means, said trammel arm means comprising a pair of vertically spaced members, at least one of said members being a beam, said base structure being provided with a pair of vertically spaced member supporting structures each provided with a guide groove, the longitudinal axes of said grooves being at right angles to each other, each beam being provided with a control element slidable in a respective guide groove, and means effective to maintain said control elements in one selective relative position whereby the trammel arm means is limited to move- I ment such that the wheel dressing means is movable only in a circular path or to maintain said control elements in any other selective relative position thereof whereby the trammel arm means is limited to movement such that the wheel dressing means is movable only in an elliptical path.

References Cited in the file of this patent UNITED STATES PATENTS 1,470,168 Iepsen Oct. 9, 1923 1,474,868 Walker Nov. 20, 1923 FOREIGN PATENTS 247,785 Germany June 7, 1912 311,548 Germany Mar. 27, 1919 

